For the visually impaired person, optical aids are available for seeing objects at distances beyond the visual resolution of the unaided eye. A conventional device has a pair of telescopic lenses mounted to the ordinary lenses in a conventional eyeglass frame. The telescopes are designed particularly for distance tasks that are to be performed while the wearer is stationary, such as watching television, theater, sporting events, or spotting distant displays, e.g. a blackboard, stock market quotes, etc., from a seat.
The telescopes typically are constructed of a system of lenses carried in a lightweight plastic housing, and are mounted to or through the ordinary lenses. For increased versatility, the telescopes can be mounted higher on the ordinary lenses, so that they are out of the way for seeing near distances through the ordinary lenses. These are called bioptic telescopes. Alternatively, reading lens caps can be removably attached to the front of the telescopes to allow the wearer to switch to working at near distances. To provide assisted vision at variable distances, the telescopes can be of the spiral expanded field (terrestrial) type which are manually adjustable for viewing from infinity to intermediate and near distances. In any event, one can also employ Galilean telescopes which are designed for distance tasks that are to be performed by a handicapped user.
The conventional telescopes have the problem that they are designed for a particular magnification power and are in focus only for a specified far distance the wearer wants to see. For nearer distances, the wearer must affix the reading caps on the telescopes, switch or remove the glasses, or manually adjust the spiral expanded field telescopes for changing distances. These devices have the common problem that they are cumbersome and disorienting for the wearer. With conventional terrestrial telescopes, the experience is analogous to the difficulty of using a pair of binoculars while switching between focusing on far and near objects.
Some optical devices, such as cameras, have automatic focusing systems for focusing an objective lens over a range of distances. However, such systems generally employ complex and costly distance measuring sensors, which are dependent on precisely locating an object to be focused on and most of these devices need to accurately locate the exact distance of the object from the camera.